A coiling drum for the above-described purpose generally comprises a longitudinal slot in which an end of the strip to be coiled is inserted, and means for clamping this end of the strip in place.
Collapsible drum members of this type, i.e., clamping elements which are adapted to recede from the surface of the drum, can be provided as movable drum segments which can be displaced, usually radially, with respect to so-called "fixed drum segments" which, while forming part of the drum and rotating therewith remain radially positioned while the movable segments are displaced to clamp the end of the strip against the fixed segment.
Various structures of this type have been proposed and different mechanisms have been used to actuate the movable segment or clamping member of the drum. These mechanisms can include fluid-operated cylinders, camming or wedge surface and lever arrangements.
One problem which has confronted substantially all of the prior-art coiling drums and, more generally, strip coilers, is the inability to effectively clamp the end of the strip in place under certain conditions and without various drawbacks. For example, when the strip is one band of a plurality of bands longitudinally separated from one another by slitting or splitting following the rolling of the strip, the bands may be of different thicknesses and the firm engagement of one strip may prevent effective engagement of thinner strips. The same defect applies when the strips arrive, not from a shear or slitting arrangement, but from different rolling units to a common coiler.
Another drawback is that an adequate seizure of an end of the strip could not be obtained unless this end were sharply bent upon insertion of the strip into the slot, this creasing operation resulting in a flaw in the strip material and, in many cases, causing kinking or like angular deformities. These flaws "print-through" to the subsequently applied turns of the strip. Yet another drawback has been the tendency of the smooth-surfaced strip to slide out of contact with the fixed clamping surface and the movable clamping surface, the former being provided in or on the fixed member while the latter is provided on the movable clamping member.
Admittedly, attempts have been made to eliminate the second problem by a rounding of the surface at which the slot in the drum merges on to the surface thereof, but this has not been found to be adequate in most instances and does not suffice to prevent defects from arising in the subsequently applied turns unless the strip is drawn with considerable tractive force to hug the rounded surface. This of course creates problems with respect to the force with which the strip must be retained by the clamping device.
Finally, it should be noted that firm gripping of the end of the strip is required to counteract the high tractive forces developing during tight cooling of the strip and this has only been possible with conventional or known band coilers when an angular bend has been formed in the clamped end of the strip. This of course gave rise to the disadvantages enumerated above. It thus has been a matter of considerable investigation to establish a technique for seizing the end of a metal strip in a band coiler without the defects mentioned.